Chip breakers for orthopaedic reamers

ABSTRACT

An orthopaedic reamer, including a generally hemispherical shell rotatable about an axis having a plurality of tongues. Each tongue partially defines a corresponding C-shaped opening with a substantially constant width. Each tongue includes a cutting segment. The cutting segment includes at least one notch and a plurality of cutting teeth. Adjacent cutting teeth are separated by a corresponding notch. Each notch of each tongue has a corresponding cutting tooth of another tongue overlapping a cutting position of the notch during rotation of the orthopaedic reamer about the axis.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 10/348,932,entitled “CHIP BREAKERS FOR ORTHOPAEDIC REAMERS”, filed Jan. 22, 2003now U.S. Pat. No. 7,118,575.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to orthopaedic reamers, and, moreparticularly, to chip breaker cutting apertures and surfaces fororthopaedic reamers.

2. Description of the Related Art

A hip joint prosthesis requires preparation of the acetabulum by millinga precision shape therein using an orthopaedic reamer. A typicalorthopaedic reamer has a hollow hemispherical shell shape with aperturesin the hemispherical shell. The hemispherical shell is attached to adriver with a shaft which can be inserted into a rotating tool such as adrill thereby providing rotation of the orthopaedic reamer, and hence,the motive force for the milling operation. The apex of thehemispherical shell typically is along the shaft longitudinal axis.

The apertures in the hemispherical shell have a dual purpose. Firstly,an edge of each aperture is formed outwardly, respective to the shellcenter, to form a cutting tooth or cutting surface. The forming of theaperture edge outwardly is referred to as a lipping operation. Secondly,the apertures allow milled tissue to collect in the shell interior,thereby providing a somewhat self-cleaning aspect to the millingoperation. The apertures and cutting surfaces are located on the shellto provide approximately 180° cutting coverage during rotation of theacetabular reamer thereby allowing a uniform milling of the acetabulum.

The size, shape, quantity and location of apertures and correspondingcutting surfaces are interrelated. For example, smaller geometryapertures and corresponding cutting surfaces require a greater quantityin the hemispherical shell to provide approximately 180° cuttingcoverage during rotation of the acetabular reamer. Conversely, fewerrelatively large size apertures and corresponding cutting surfaces arerequired to provide the same cutting coverage. The size and shape of thecutting apertures also influences the location of the apertures. Forexample, one known design of acetabular reamer has approximately 0.2inch diameter round apertures arranged in a spiral pattern in the reamerhemispherical shell.

When the reamer is used to prepare the acetabulum for hip jointprosthesis, variation in the size of the acetabulum for the humanpopulation requires a range of sizes of acetabular reamers, a specificsize of the acetabular reamer being determined by the hip joint size ofthe person undergoing hip joint prosthesis. The different sizes ofacetabular reamers are generally specified by different radii ofcurvature, or diameters, of the hemispherical shell. For a given sizeand shape for apertures and corresponding cutting surfaces, a largerreamer size requires a larger quantity, and possibly differentlocations.

Manufacturing cost for a reamer is incremented for additional aperturesand corresponding cutting surfaces; therefore, larger and fewer cuttingapertures save manufacturing cost. When the reamer is used to preparethe acetabulum for hip joint prosthesis, a rotary hand tool provides themotive force and is connected to a driver which is connected to areamer. In use, larger cutting surfaces remove more material for a givenrotation of the tool leading to vibration or chattering. This vibrationor chattering can degrade cutting performance by making the rotarytool-driver-reamer combination harder for the operator (surgeon) tocontrol. Smaller cutting surfaces remove smaller pieces of material,thereby improving the vibration characteristics of the rotarytool-driver-reamer combination, but require a larger quantity of cuttingsurfaces, thereby increasing the manufacturing cost of the reamer. Inother words, there is a trade-off between the manufacturing efficiencyof fewer, larger cutting apertures and the cutting and vibrationperformance of a greater number of, and smaller, cutting apertures.

What is needed in the art are reamer apertures and corresponding cuttingsurfaces with the manufacturing efficiency of larger cutting aperturesand the cutting, chip breaking and vibration performance of smallercutting apertures.

SUMMARY OF THE INVENTION

The present invention provides orthopaedic reamer cutting surfaces withnotches separating the cutting teeth. Each cutting tooth has a cuttingsurface associated with a corresponding C-shaped opening with asubstantially constant width.

The invention comprises, in one form thereof, an orthopaedic reamerincluding a generally hemispherical shell having a plurality of tongues.Each tongue partially defines a corresponding C-shaped opening with asubstantially constant width. Each tongue includes a cutting segment.The cutting segment includes at least one notch and a plurality ofcutting teeth. Adjacent cutting teeth are separated by a correspondingnotch.

An advantage of the present invention is an orthopaedic reamer withapertures and corresponding cutting surfaces having the manufacturingefficiency of larger cutting apertures.

Another advantage is an orthopaedic reamer with larger cutting aperturesand the cutting, chip breaking and vibration performance of smallercutting apertures.

Yet another advantage is the general shape of the C-shaped opening lendsitself to modern efficient machining processes further improving theproduction efficiency of the orthopaedic reamer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of an embodiment of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a perspective view of an embodiment of an orthopaedic reamerof the present invention;

FIG. 2 is a side view of the orthopaedic reamer shown in FIG. 1;

FIG. 3 is a cross-sectional view taken along section line 3—3 in FIG. 2;and

FIG. 4 is a top view of the orthopaedic reamer shown in FIG. 1.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplification set out hereinillustrates one preferred embodiment of the invention, in one form, andsuch exemplification is not to be construed as limiting the scope of theinvention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there isshown an orthopaedic reamer 10 which generally includes hemisphericalshell 12 having a plurality of C-shaped openings 14 and a plurality oftongues 18.

C-shaped opening 14 include release slots 26 and cutting aperture 28.Release slots 26 and cutting apertures 28 have a substantially constantwidth. Release slots 26 allow the forming of tongue 18 outward fromhemispherical shell 12 at bend 30. The angle between release slots 26and cutting aperture 28 is approximately 90°, however, other anglesvarying from 0° to 180° are possible. Alternatively, release slots 26and cutting aperture 28 can form a continuously curved C-shaped openings14. C-shaped openings 14 can alternatively include a plurality ofrelease slots 26 located at either end of cutting aperture 28. C-shapedopenings 14 are located on hemispherical shell 12 to provideapproximately 180° cutting coverage during rotation of the orthopaedicreamer 10 thereby allowing a uniform milling of, for example, anacetabulum.

Tongue 18 includes cutting segment 20. Each tongue 18, along withhemispherical shell 12, defines a corresponding C-shaped opening 14therebetween. Cutting segment 20 includes at least one notch 22 and aplurality of cutting teeth 24. Adjacent cutting teeth 24 are separatedby a corresponding notch 22. Notch 22 can be a variety of shapesincluding at least partially rectangular, triangular, polygonal,circular, parabolic, elliptical, a combination of curved segments and/ora combination of curved and straight segments. The width of notch 22 isless than the width of tooth 24.

In order to provide 180° cutting coverage during rotation of theorthopaedic reamer 10, L-shaped openings 40 are provided proximate tohemisphere base 34. L-shaped openings 40 are similar to C-shaped opening14 with the exception that release edge 42 in L-shaped openings 40replaces one of release slots 26. Each L-shaped opening 40 isessentially a partial C-shaped opening 14 with second tongue 44essentially a partial tongue 18 and second cutting aperture 46 a partialcutting aperture 28. The angle between release edge 42 and secondcutting aperture 46 is approximately 90°; however, other angles varyingfrom 0° to 180° are possible. The angle between release slots 26 andsecond cutting aperture 46 is approximately 90°; however, other anglesvarying from 0° to 180° are possible. L-shaped openings 40 arenecessitated, in part, by the requirement that during rotation oforthopaedic reamer 10, any notch 22 must be overlapped by at least onecutting tooth. This requirement eliminates grooves in the machinedelement (not shown) such as an acetabulum. For a given radius forhemispherical shell 12 and a given size for C-shaped opening 14,placement of C-shaped openings 14 to provide 180° cutting coverageduring rotation of the orthopaedic reamer 10 results in partial C-shapedopenings near hemisphere base 34, hence the L-shaped openings 40 inorthopaedic reamer 10. Depending on the position of L-shaped opening oropenings 40 on hemispherical shell 12, a corresponding cutting segmentcan include a single tooth or partial tooth with no corresponding notch.

The alternate shapes of notch 22 described above can result in alternateshapes of cutting segment 20, such as a wave shape.

Referring to FIG. 3, cutting edge 32 is formed during the fabrication ofC-shaped opening 14 or L-shaped opening 40, and further during theforming of tongue 18 or second tongue 44 outward from hemisphericalshell 12. Cutting edge 32 can be a variety of cross-sectional shapesincluding at least partially rectangular, triangular, polygonal,circular, parabolic, elliptical, a combination of curved segments and/ora combination of curved and straight segments.

In use, orthopaedic reamer 10 is attached to a driver (not shown) with ashaft which can be inserted into a rotating tool (not shown) such as adrill thereby providing rotation of orthopaedic reamer 10. An operator(a surgeon, not shown) uses orthopaedic reamer 10 to prepare anorthopaedic element of the patient (not shown). If the operation is hipjoint prosthesis, the acetabulum (not shown) is prepared by milling aprecision shape therein using orthopaedic reamer 10.

As can be best seen in FIGS. 1, 2 and 4, the relatively large size ofC-shaped opening 14 and L-shape opening 40 allows for fewer suchopenings in hemispherical shell 12, thereby reducing manufacturing costsfor orthopaedic reamer 10. The relatively large cutting segment 20 isseparated into a plurality of smaller cutting teeth 24 and correspondingnotch or notches 22 thereby breaking removed material into smaller chipsand giving orthopaedic reamer 10 the cutting, chip breaking andvibration performance of smaller cutting apertures and surfaces. Thegeneral shape of C-shaped opening 14 and L-shape opening 40 lends itselfto modern efficient machining processes further improving the productionefficiency of orthopaedic reamer 10.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

1. An orthopaedic reamer, comprising: a generally hemispherical shellrotatable about an axis, including at least three tongues, each saidtongues partially defining a corresponding C-shaped opening with asubstantially constant width, each said tongues including a cuttingsegment, said cutting segment including at least one notch and aplurality of cutting teeth, adjacent said cutting teeth separated by acorresponding said notch, each notch of each said tongue having acorresponding one of said plurality of cutting teeth of another tongueoverlapping a cutting position of said at least one notch duringrotation of the orthopaedic reamer about said axis.
 2. The orthopaedicreamer of claim 1, wherein said C-shaped opening includes a plurality ofrelease slots and a cutting aperture therebetween.
 3. The orthopaedicreamer of claim 2, including an angle of approximately 90° between saidrelease slots and said cutting aperture.
 4. The orthopaedic reamer ofclaim 2, wherein said plurality of release slots each have a releaseslot width, said cutting aperture has a cutting aperture width, and saidrelease slot width is approximately equal to said cutting aperturewidth.
 5. The orthopaedic reamer of claim 1, wherein each said notch hasa notch width, each said cutting tooth has a cutting tooth width, andsaid cutting tooth width is wider than said notch width.
 6. Anorthopaedic reamer, comprising: a generally hemispherical shellrotatable about an axis, including at least three tongues, at least oneof said tongues partially defining a corresponding L-shaped opening witha substantially constant width, each said tongue including a cuttingsegment, said cutting segment including at least one notch and aplurality of cutting teeth, adjacent said cutting teeth separated by acorresponding said notch, each of said at least one notch of each saidtongue having a corresponding one of said plurality of cutting teeth ofanother tongue overlapping a cutting position of said at least one notchduring rotation of the orthopaedic reamer about said axis.
 7. Theorthopaedic reamer of claim 6, wherein said L-shaped opening includes arelease slot, a release edge and a cutting aperture therebetween.
 8. Theorthopaedic reamer of claim 7, including an angle of approximately 90°between said release slots and said cutting aperture.
 9. The orthopaedicreamer of claim 7, wherein said release slot has a release slot width,said cutting aperture has a cutting aperture width, and said releaseslot width is approximately equal to said cutting aperture width. 10.The orthopaedic reamer of claim 6, wherein each said notch has a notchwidth, each said cutting tooth has a cutting tooth width, and saidcutting tooth width is wider than said notch width.
 11. The orthopaedicreamer of claim 7, wherein said release edge and said cutting aperturehave an angle therebetween of approximately
 900. 12. A method forproviding a cutting feature in an orthopaedic reamer, comprising thesteps of: providing a generally hemispherical shell rotatable about anaxis; fabricating a plurality of generally C-shaped openings in saidhemispherical shell thereby producing at least three tongues in saidhemispherical shell, each said C-shaped opening having a substantiallyconstant width and defining a corresponding said tongue; notching acutting segment in each said tongue thereby improving the cutting andchip breaking performance of said orthopaedic reamer, each said cuttingsegment including at least one notch and a plurality of cutting teeth,each said notch having a notch width, each said cutting tooth having acutting tooth width, said cutting tooth width wider than said notchwidth; and forming said cutting segment in a direction away from saidhemispherical shell center; and positioning each notch of each saidtongue to have a corresponding one of said plurality of cutting teeth ofanother tongue overlapping a cutting position of said at least one notchduring rotation of the orthopaedic reamer about said axis.
 13. Themethod of claim 12, wherein said fabricating step includes fabricatingin said C-shaped opening a plurality of release slots and a cuttingaperture therebetween.